On May 1, 1707, the Kingdom of England (including Wales) and the Kingdom of Scotland merged as a political union known as the United Kingdom of Great Britain. This is the result of agreed terms, signed by parliaments of England and Scotland, under the Treaty of Union. Queen Anne is the first monarch of the United Kingdom of Great Britain.

The Act of Union 1800 merged the Kingdom of Great Britain with the Kingdom of Ireland to create the United Kingdom of Great Britain and Ireland On January 1, 1801. This is the result of several centuries of historic events including the invasions of ruling Normans in Ireland, the Irish Rebellion of 1641, and War of American Independence. The union eliminated the separate Parliaments of Great Britain and Ireland creating an integrated Parliament of the United Kingdom. Ireland sent roughly 100 MPs to the House of Commons and 28 peers to the House of Lords.

During the 19th and early 20th century, the rise of Irish Nationalism emerged particularly in the Catholic population. Movement for the cancellation of the Act of Union is known as “Home Rule” and many campaigns have failed including the one in 1912 that passed the House of Commons but was voted out in the House of Lords. In 1916, an one-sidedly declared “Irish Republic” was announced in Dublin and resulted to the Anglo-Irish War that lasts until 1921. The Anglo-Irish Treaty of 1921 formed the Irish Free State and left the British Commonwealth without constitutional ties with UK and 6 northern Irish counties remained part of the United Kingdom. The Royal and Parliamentary Titles Act 1927 renamed the United Kingdom of Great Britain and Ireland to United Kingdom of Great Britain and Northern Ireland.